UnusedVariables: Fix FP for unknown variable

lib/astutils.cpp

@@ -1170,6 +1170,11 @@ bool FwdAnalysis::isGlobalData(const Token *expr) const
     bool globalData = false;
     visitAstNodes(expr,
     [&](const Token *tok) {
+        if (tok->varId() && !tok->variable()) {
+            // Bailout, this is probably global
+            globalData = true;
+            return ChildrenToVisit::none;
+        }
         if (tok->originalName() == "->") {
             // TODO check if pointer points at local data
             globalData = true;

test/testunusedvar.cpp

@@ -4294,6 +4294,14 @@ private:
             "}"
         );
         ASSERT_EQUALS("", errout.str());
+
+        // Unknown variable
+        functionVariableUsage(
+            "void A::b(Date& result) {"
+            "  result = 12;\n"
+            "}"
+        );
+        ASSERT_EQUALS("", errout.str());
     }
 };